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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-COPY"
>31.8. Functions Associated with the <TT
CLASS="COMMAND"
>COPY</TT
> Command</A
></H1
><P
>   The <TT
CLASS="COMMAND"
>COPY</TT
> command in
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> has options to read from or write
   to the network connection used by <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>.
   The functions described in this section allow applications to take
   advantage of this capability by supplying or consuming copied data.
  </P
><P
>   The overall process is that the application first issues the SQL
   <TT
CLASS="COMMAND"
>COPY</TT
> command via <CODE
CLASS="FUNCTION"
>PQexec</CODE
> or one
   of the equivalent functions.  The response to this (if there is no
   error in the command) will be a <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object bearing
   a status code of <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
> or
   <TT
CLASS="LITERAL"
>PGRES_COPY_IN</TT
> (depending on the specified copy
   direction).  The application should then use the functions of this
   section to receive or transmit data rows.  When the data transfer is
   complete, another <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object is returned to indicate
   success or failure of the transfer.  Its status will be
   <TT
CLASS="LITERAL"
>PGRES_COMMAND_OK</TT
> for success or
   <TT
CLASS="LITERAL"
>PGRES_FATAL_ERROR</TT
> if some problem was encountered.
   At this point further SQL commands can be issued via
   <CODE
CLASS="FUNCTION"
>PQexec</CODE
>.  (It is not possible to execute other SQL
   commands using the same connection while the <TT
CLASS="COMMAND"
>COPY</TT
>
   operation is in progress.)
  </P
><P
>   If a <TT
CLASS="COMMAND"
>COPY</TT
> command is issued via
   <CODE
CLASS="FUNCTION"
>PQexec</CODE
> in a string that could contain additional
   commands, the application must continue fetching results via
   <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> after completing the <TT
CLASS="COMMAND"
>COPY</TT
>
   sequence.  Only when <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> returns
   <TT
CLASS="SYMBOL"
>NULL</TT
> is it certain that the <CODE
CLASS="FUNCTION"
>PQexec</CODE
>
   command string is done and it is safe to issue more commands.
  </P
><P
>   The functions of this section should be executed only after obtaining
   a result status of <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
> or
   <TT
CLASS="LITERAL"
>PGRES_COPY_IN</TT
> from <CODE
CLASS="FUNCTION"
>PQexec</CODE
> or
   <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
>.
  </P
><P
>   A <TT
CLASS="STRUCTNAME"
>PGresult</TT
> object bearing one of these status values
   carries some additional data about the <TT
CLASS="COMMAND"
>COPY</TT
> operation
   that is starting.  This additional data is available using functions
   that are also used in connection with query results:

   <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQNFIELDS-1"
></A
><CODE
CLASS="FUNCTION"
>PQnfields</CODE
>
      </DT
><DD
><P
>       Returns the number of columns (fields) to be copied.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQBINARYTUPLES-1"
></A
><CODE
CLASS="FUNCTION"
>PQbinaryTuples</CODE
>
      </DT
><DD
><P
>       0 indicates the overall copy format is textual (rows separated by
       newlines, columns separated by separator characters, etc).  1
       indicates the overall copy format is binary.  See <A
HREF="sql-copy.html"
>COPY</A
> for more information.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQFFORMAT-1"
></A
><CODE
CLASS="FUNCTION"
>PQfformat</CODE
>
      </DT
><DD
><P
>       Returns the format code (0 for text, 1 for binary) associated with
       each column of the copy operation.  The per-column format codes
       will always be zero when the overall copy format is textual, but
       the binary format can support both text and binary columns.
       (However, as of the current implementation of <TT
CLASS="COMMAND"
>COPY</TT
>,
       only binary columns appear in a binary copy; so the per-column
       formats always match the overall format at present.)
      </P
></DD
></DL
></DIV
><P>
  </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    These additional data values are only available when using protocol
    3.0.  When using protocol 2.0, all these functions will return 0.
   </P
></BLOCKQUOTE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-COPY-SEND"
>31.8.1. Functions for Sending <TT
CLASS="COMMAND"
>COPY</TT
> Data</A
></H2
><P
>    These functions are used to send data during <TT
CLASS="LITERAL"
>COPY FROM
    STDIN</TT
>.  They will fail if called when the connection is not in
    <TT
CLASS="LITERAL"
>COPY_IN</TT
> state.
   </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQPUTCOPYDATA"
></A
><CODE
CLASS="FUNCTION"
>PQputCopyData</CODE
>
      </DT
><DD
><P
>       Sends data to the server during <TT
CLASS="LITERAL"
>COPY_IN</TT
> state.
</P><PRE
CLASS="SYNOPSIS"
>int PQputCopyData(PGconn *conn,
                  const char *buffer,
                  int nbytes);</PRE
><P>
      </P
><P
>       Transmits the <TT
CLASS="COMMAND"
>COPY</TT
> data in the specified
       <TT
CLASS="PARAMETER"
>buffer</TT
>, of length <TT
CLASS="PARAMETER"
>nbytes</TT
>, to the server.
       The result is 1 if the data was sent, zero if it was not sent
       because the attempt would block (this case is only possible if the
       connection is in nonblocking mode), or -1 if an error occurred.
       (Use <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to retrieve details if
       the return value is -1.  If the value is zero, wait for write-ready
       and try again.)
      </P
><P
>       The application can divide the <TT
CLASS="COMMAND"
>COPY</TT
> data stream
       into buffer loads of any convenient size.  Buffer-load boundaries
       have no semantic significance when sending.  The contents of the
       data stream must match the data format expected by the
       <TT
CLASS="COMMAND"
>COPY</TT
> command; see <A
HREF="sql-copy.html"
>COPY</A
> for details.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQPUTCOPYEND"
></A
><CODE
CLASS="FUNCTION"
>PQputCopyEnd</CODE
>
      </DT
><DD
><P
>       Sends end-of-data indication to the server during <TT
CLASS="LITERAL"
>COPY_IN</TT
> state.
</P><PRE
CLASS="SYNOPSIS"
>int PQputCopyEnd(PGconn *conn,
                 const char *errormsg);</PRE
><P>
      </P
><P
>       Ends the <TT
CLASS="LITERAL"
>COPY_IN</TT
> operation successfully if
       <TT
CLASS="PARAMETER"
>errormsg</TT
> is <TT
CLASS="SYMBOL"
>NULL</TT
>.  If
       <TT
CLASS="PARAMETER"
>errormsg</TT
> is not <TT
CLASS="SYMBOL"
>NULL</TT
> then the
       <TT
CLASS="COMMAND"
>COPY</TT
> is forced to fail, with the string pointed to by
       <TT
CLASS="PARAMETER"
>errormsg</TT
> used as the error message.  (One should not
       assume that this exact error message will come back from the server,
       however, as the server might have already failed the
       <TT
CLASS="COMMAND"
>COPY</TT
> for its own reasons.  Also note that the option
       to force failure does not work when using pre-3.0-protocol
       connections.)
      </P
><P
>       The result is 1 if the termination data was sent, zero if it was
       not sent because the attempt would block (this case is only possible
       if the connection is in nonblocking mode), or -1 if an error
       occurred.  (Use <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to retrieve
       details if the return value is -1.  If the value is zero, wait for
       write-ready and try again.)
      </P
><P
>       After successfully calling <CODE
CLASS="FUNCTION"
>PQputCopyEnd</CODE
>, call
       <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> to obtain the final result status of the
       <TT
CLASS="COMMAND"
>COPY</TT
> command.  One can wait for this result to be
       available in the usual way.  Then return to normal operation.
      </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-COPY-RECEIVE"
>31.8.2. Functions for Receiving <TT
CLASS="COMMAND"
>COPY</TT
> Data</A
></H2
><P
>    These functions are used to receive data during <TT
CLASS="LITERAL"
>COPY TO
    STDOUT</TT
>.  They will fail if called when the connection is not in
    <TT
CLASS="LITERAL"
>COPY_OUT</TT
> state.
   </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQGETCOPYDATA"
></A
><CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
>
      </DT
><DD
><P
>       Receives data from the server during <TT
CLASS="LITERAL"
>COPY_OUT</TT
> state.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetCopyData(PGconn *conn,
                  char **buffer,
                  int async);</PRE
><P>
      </P
><P
>       Attempts to obtain another row of data from the server during a
       <TT
CLASS="COMMAND"
>COPY</TT
>.  Data is always returned one data row at
       a time; if only a partial row is available, it is not returned.
       Successful return of a data row involves allocating a chunk of
       memory to hold the data.  The <TT
CLASS="PARAMETER"
>buffer</TT
> parameter must
       be non-<TT
CLASS="SYMBOL"
>NULL</TT
>.  <TT
CLASS="PARAMETER"
>*buffer</TT
> is set to
       point to the allocated memory, or to <TT
CLASS="SYMBOL"
>NULL</TT
> in cases
       where no buffer is returned.  A non-<TT
CLASS="SYMBOL"
>NULL</TT
> result
       buffer should be freed using <CODE
CLASS="FUNCTION"
>PQfreemem</CODE
> when no longer
       needed.
      </P
><P
>       When a row is successfully returned, the return value is the number
       of data bytes in the row (this will always be greater than zero).
       The returned string is always null-terminated, though this is
       probably only useful for textual <TT
CLASS="COMMAND"
>COPY</TT
>.  A result
       of zero indicates that the <TT
CLASS="COMMAND"
>COPY</TT
> is still in
       progress, but no row is yet available (this is only possible when
       <TT
CLASS="PARAMETER"
>async</TT
> is true).  A result of -1 indicates that the
       <TT
CLASS="COMMAND"
>COPY</TT
> is done.  A result of -2 indicates that an
       error occurred (consult <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> for the reason).
      </P
><P
>       When <TT
CLASS="PARAMETER"
>async</TT
> is true (not zero),
       <CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> will not block waiting for input; it
       will return zero if the <TT
CLASS="COMMAND"
>COPY</TT
> is still in progress
       but no complete row is available.  (In this case wait for read-ready
       and then call <CODE
CLASS="FUNCTION"
>PQconsumeInput</CODE
> before calling
       <CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> again.)  When <TT
CLASS="PARAMETER"
>async</TT
> is
       false (zero), <CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> will block until data is
       available or the operation completes.
      </P
><P
>       After <CODE
CLASS="FUNCTION"
>PQgetCopyData</CODE
> returns -1, call
       <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> to obtain the final result status of the
       <TT
CLASS="COMMAND"
>COPY</TT
> command.  One can wait for this result to be
       available in the usual way.  Then return to normal operation.
      </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LIBPQ-COPY-DEPRECATED"
>31.8.3. Obsolete Functions for <TT
CLASS="COMMAND"
>COPY</TT
></A
></H2
><P
>    These functions represent older methods of handling <TT
CLASS="COMMAND"
>COPY</TT
>.
    Although they still work, they are deprecated due to poor error handling,
    inconvenient methods of detecting end-of-data, and lack of support for binary
    or nonblocking transfers.
   </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQGETLINE"
></A
><CODE
CLASS="FUNCTION"
>PQgetline</CODE
>
      </DT
><DD
><P
>       Reads  a  newline-terminated  line  of  characters (transmitted
       by the server) into a buffer string of size <TT
CLASS="PARAMETER"
>length</TT
>.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetline(PGconn *conn,
              char *buffer,
              int length);</PRE
><P>
      </P
><P
>       This function copies up to <TT
CLASS="PARAMETER"
>length</TT
>-1 characters into
       the buffer and converts the terminating newline into a zero byte.
       <CODE
CLASS="FUNCTION"
>PQgetline</CODE
> returns <TT
CLASS="SYMBOL"
>EOF</TT
> at the
       end of input, 0 if the entire line has been read, and 1 if the
       buffer is full but the terminating newline has not yet been read.
       </P
><P
>       Note that the application must check to see if a new line consists
       of  the  two characters  <TT
CLASS="LITERAL"
>\.</TT
>, which  indicates
       that the server has finished sending the results  of  the
       <TT
CLASS="COMMAND"
>COPY</TT
> command.  If  the  application might receive
       lines that are more than <TT
CLASS="PARAMETER"
>length</TT
>-1  characters  long,
       care is needed to be sure it recognizes the <TT
CLASS="LITERAL"
>\.</TT
>
       line correctly (and does not, for example, mistake the end of a
       long data line for a terminator line).
      </P
></DD
><DT
><A
NAME="LIBPQ-PQGETLINEASYNC"
></A
><CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
>
      </DT
><DD
><P
>       Reads a row of <TT
CLASS="COMMAND"
>COPY</TT
> data (transmitted  by the
       server) into a buffer without blocking.
</P><PRE
CLASS="SYNOPSIS"
>int PQgetlineAsync(PGconn *conn,
                   char *buffer,
                   int bufsize);</PRE
><P>
      </P
><P
>       This function is similar to <CODE
CLASS="FUNCTION"
>PQgetline</CODE
>, but it can be used
       by applications
       that must read <TT
CLASS="COMMAND"
>COPY</TT
> data asynchronously, that is, without blocking.
       Having issued the <TT
CLASS="COMMAND"
>COPY</TT
> command and gotten a <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
>
       response, the
       application should call <CODE
CLASS="FUNCTION"
>PQconsumeInput</CODE
> and
       <CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
> until the
       end-of-data signal is detected.
       </P
><P
>       Unlike <CODE
CLASS="FUNCTION"
>PQgetline</CODE
>, this function takes
       responsibility for detecting end-of-data.
      </P
><P
>       On each call, <CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
> will return data if a
       complete data row is available in <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>'s input buffer.
       Otherwise, no data is returned until the rest of the row arrives.
       The function returns -1 if the end-of-copy-data marker has been recognized,
       or 0 if no data is available, or a positive number giving the number of
       bytes of data returned.  If -1 is returned, the caller must next call
       <CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>, and then return to normal processing.
      </P
><P
>       The data returned will not extend beyond a data-row boundary.  If possible
       a whole row will be returned at one time.  But if the buffer offered by
       the caller is too small to hold a row sent by the server, then a partial
       data row will be returned.  With textual data this can be detected by testing
       whether the last returned byte is <TT
CLASS="LITERAL"
>\n</TT
> or not.  (In a binary
       <TT
CLASS="COMMAND"
>COPY</TT
>, actual parsing of the <TT
CLASS="COMMAND"
>COPY</TT
> data format will be needed to make the
       equivalent determination.)
       The returned string is not null-terminated.  (If you want to add a
       terminating null, be sure to pass a <TT
CLASS="PARAMETER"
>bufsize</TT
> one smaller
       than the room actually available.)
      </P
></DD
><DT
><A
NAME="LIBPQ-PQPUTLINE"
></A
><CODE
CLASS="FUNCTION"
>PQputline</CODE
>
      </DT
><DD
><P
>       Sends  a  null-terminated  string  to  the server.  Returns 0 if
       OK and <TT
CLASS="SYMBOL"
>EOF</TT
> if unable to send the string.
</P><PRE
CLASS="SYNOPSIS"
>int PQputline(PGconn *conn,
              const char *string);</PRE
><P>
      </P
><P
>       The <TT
CLASS="COMMAND"
>COPY</TT
> data stream sent by a series of calls
       to <CODE
CLASS="FUNCTION"
>PQputline</CODE
> has the same format as that
       returned by <CODE
CLASS="FUNCTION"
>PQgetlineAsync</CODE
>, except that
       applications are not obliged to send exactly one data row per
       <CODE
CLASS="FUNCTION"
>PQputline</CODE
> call; it is okay to send a partial
       line or multiple lines per call.
      </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>        Before <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> protocol 3.0, it was necessary
        for the application to explicitly send the two characters
        <TT
CLASS="LITERAL"
>\.</TT
> as a final line to indicate to the server that it had
        finished sending <TT
CLASS="COMMAND"
>COPY</TT
> data.  While this still works, it is deprecated and the
        special meaning of <TT
CLASS="LITERAL"
>\.</TT
> can be expected to be removed in a
        future release.  It is sufficient to call <CODE
CLASS="FUNCTION"
>PQendcopy</CODE
> after
        having sent the actual data.
       </P
></BLOCKQUOTE
></DIV
></DD
><DT
><A
NAME="LIBPQ-PQPUTNBYTES"
></A
><CODE
CLASS="FUNCTION"
>PQputnbytes</CODE
>
      </DT
><DD
><P
>       Sends  a  non-null-terminated  string  to  the server.  Returns
       0 if OK and <TT
CLASS="SYMBOL"
>EOF</TT
> if unable to send the string.
</P><PRE
CLASS="SYNOPSIS"
>int PQputnbytes(PGconn *conn,
                const char *buffer,
                int nbytes);</PRE
><P>
      </P
><P
>       This is exactly like <CODE
CLASS="FUNCTION"
>PQputline</CODE
>, except that the data
       buffer need not be null-terminated since the number of bytes to send is
       specified directly.  Use this procedure when sending binary data.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQENDCOPY"
></A
><CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>
      </DT
><DD
><P
>       Synchronizes with the server.
</P><PRE
CLASS="SYNOPSIS"
>int PQendcopy(PGconn *conn);</PRE
><P>
       This function waits until the  server  has  finished  the copying.
       It should either be issued when the  last  string  has  been sent
       to  the  server using <CODE
CLASS="FUNCTION"
>PQputline</CODE
> or when the
       last string has been  received  from  the  server using
       <CODE
CLASS="FUNCTION"
>PGgetline</CODE
>.  It must be issued or the server
       will get <SPAN
CLASS="QUOTE"
>"out of sync"</SPAN
> with  the client.   Upon return
       from this function, the server is ready to receive the next SQL
       command.  The return value is 0  on  successful  completion,
       nonzero otherwise.  (Use <CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> to
       retrieve details if the return value is nonzero.)
      </P
><P
>       When using <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
>, the application should
       respond to a <TT
CLASS="LITERAL"
>PGRES_COPY_OUT</TT
> result by executing
       <CODE
CLASS="FUNCTION"
>PQgetline</CODE
> repeatedly, followed by
       <CODE
CLASS="FUNCTION"
>PQendcopy</CODE
> after the terminator line is seen.
       It should then return to the <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> loop
       until <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> returns a null pointer.
       Similarly a <TT
CLASS="LITERAL"
>PGRES_COPY_IN</TT
> result is processed
       by a series of <CODE
CLASS="FUNCTION"
>PQputline</CODE
> calls followed by
       <CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>, then return to the
       <CODE
CLASS="FUNCTION"
>PQgetResult</CODE
> loop.  This arrangement will
       ensure that a <TT
CLASS="COMMAND"
>COPY</TT
> command embedded in a series
       of <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> commands will be executed correctly.
      </P
><P
>       Older applications are likely to submit a <TT
CLASS="COMMAND"
>COPY</TT
>
       via <CODE
CLASS="FUNCTION"
>PQexec</CODE
> and assume that the transaction
       is done after <CODE
CLASS="FUNCTION"
>PQendcopy</CODE
>.  This will work
       correctly only if the <TT
CLASS="COMMAND"
>COPY</TT
> is the only
       <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> command in the command string.
      </P
></DD
></DL
></DIV
></DIV
></DIV
><DIV
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><HR
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SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="libpq-notify.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="libpq-control.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Asynchronous Notification</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="libpq.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Control Functions</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>